packer_test: add remote install with pre-rel test

Remotely installing plugins with a pre-release as part of the constraint
is unsupported by Packer, and should error if that happens.
This test makes sure that this gets treated as an error if that's the
case, even before attempting to connect to the source.

packer_test/install_test.go

@@ -77,10 +77,24 @@ func (ts *PackerTestSuite) TestRemoteInstallWithPluginsInstall() {
 			SetArgs("plugins", "install", "github.com/hashicorp/hashicups").
 			Assert(MustSucceed())
 	})
+}
+
+func (ts *PackerTestSuite) TestRemoteInstallOfPreReleasePlugin() {
+	pluginPath, cleanup := ts.MakePluginDir()
+	defer cleanup()
+
+	ts.Run("try to init with a pre-release constraint - should fail", func() {
+		ts.PackerCommand().UsePluginDir(pluginPath).
+			SetArgs("init", "templates/pre-release_constraint.pkr.hcl").
+			Assert(MustFail(),
+				Grep("Invalid version constraint", grepStdout),
+				Grep("Unsupported prerelease for constraint", grepStdout))
+	})
 
-	ts.Run("install dev version of a remote plugin with packer plugins install - must fail", func() {
+	ts.Run("try to plugins install with a pre-release version - should fail", func() {
 		ts.PackerCommand().UsePluginDir(pluginPath).
-			SetArgs("plugins", "install", "github.com/hashicorp/hashicups", "v1.0.2-dev").
-			Assert(MustFail(), Grep("Remote installation of pre-release plugin versions is unsupported.", grepStdout))
+			SetArgs("plugin", "install", "github.com/hashicorp/hashicups", "1.0.2-dev").
+			Assert(MustFail(),
+				Grep("Unsupported prerelease for constraint", grepStdout))
 	})
 }

packer_test/templates/pre-release_constraint.pkr.hcl

@@ -0,0 +1,14 @@
+packer {
+	required_plugins {
+		tester = {
+			source = "github.com/hashicorp/hashicups"
+			version = "= 1.0.2-dev"
+		}
+	}
+}
+
+source "tester-dynamic" "test" {}
+
+build {
+	sources = ["tester-dynamic.test"]
+}